Compositions and methods for coating food cans

ABSTRACT

A composition for coating food cans is disclosed. The composition comprises a polyester, an acrylic copolymer and a crosslinker; the polyester and acrylic copolymer have been compatibilized in some way, such as through graft copolymerization. Methods for compatibilizing acrylics and polyesters are also disclosed as are methods for coating cans using compositions comprising acrylic and polyesters.

CROSS-REFERENCE TO RELATED APPLICATION

This patent application is a Division of U.S. patent application Ser.No. 10/231,652 filed Aug. 30, 2002, entitled “COMPOSITIONS AND METHODSFOR COATING FOOD CANS”.

FIELD OF THE INVENTION

The present invention relates to compositions and methods for coatingmetal. More specifically, the present invention relates to compositionsand methods for coating food cans, wherein the coating compositionscomprise polyester and acrylic polymers.

BACKGROUND OF THE INVENTION

The application of various treatment and pretreatment solutions tometals to retard or inhibit corrosion is well established. This isparticularly true in the area of metal food and beverage cans. Coatingsare applied to the interior of such containers to prevent the contentsfrom contacting the metal of the container. Contact between the metaland the food or beverage can lead to corrosion of the metal container,which can then contaminate the food or beverage. This is particularlytrue when the contents of the can are acidic in nature, such astomato-based products and soft drinks. The coatings applied to theinterior of food and beverage cans also helps prevent corrosion in thehead space of the cans, which is the area between the fill line of thefood product and the can lid; corrosion in the head space isparticularly problematic with food products having a high salt content.

Various epoxy-based coatings and polyvinyl chloride-based coatings havebeen used in the past to coat the interior of metal cans to preventcorrosion. The recycling of materials containing polyvinyl chloride orrelated halide-containing vinyl polymers can generate toxic by-products,however; moreover, these polymers are typically formulated withepoxy-functional plasticizers. In addition, epoxy-based coatings areprepared from monomers such as bisphenol A and bisphenol Adiglycidylether (“BADGE”), which is being reported as having negativehealth effects. While attempts have been made to scavenge the residualunreacted epoxy with, for example, acid functional polymers, this doesnot adequately address the problem; some free BADGE or its by-productswill still remain. Government authorities, particularly in Europe, arebecoming even more restrictive on the amount of free BADGE or itsby-products that are acceptable. Thus, there is a need for food andbeverage can liners that are virtually free from BADGE, epoxy and vinylproducts.

SUMMARY OF THE INVENTION

The present invention is directed to compositions and methods forcoating the inside of food cans. The term “food cans” is used herein torefer to cans, containers or any type of metal receptacle used to holdany type of food or beverage. The methods generally involve coating thecans with a composition comprising a polyester and an acrylic polyol.

As will be appreciated in the art, polyester coatings are good forflexibility, but are subject to hydrolysis in acid environments. Incontrast, acrylics are good for providing resistance, but areinflexible. The use of either polyester or acrylic copolymers alone,therefore, has drawbacks. Their use together, however, is sometimesproblematic because polyester and acrylic are often incompatible. Theiruse together in the present invention therefore requires that they bemade compatible in some way; methods for doing so are described hereinand are the further subject of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to compositions for coating food canscomprising an acrylic copolymer; a polyester; and a crosslinker. Thepolyester and acrylic copolymer should be made compatible to form thepresent compositions. This can be accomplished by any of various methodsknown in the art or described herein, including but not limited toemploying blending techniques known in the art, preparinginterpenetrating networks, or forming a graft copolymer. In oneembodiment, the compositions are “epoxy-free”. “Epoxy-free” means thatboth the polyester and acrylic portion of the composition are free fromoxirane rings or residues of oxirane rings; bisphenol A; BADGE oradducts of BADGE. The coating composition is also free ofpolyvinylchloride or related halide-containing vinyl polymers.

The polyester component used in the present methods can be prepared byconventional means such as polyesterification of a polycarboxylic acidor anhydride with a polyol using techniques known to those skilled inthe art. Usually, the polycarboxylic acids and polyols are aliphatic oraromatic dibasic acids and diols, although the invention is not solimited. Transesterification of polycarboxylic acid esters usingconventional techniques is also possible.

Typically, the weight average molecular weight (“Mw”) of the polyesterwill range from 4,000 to 20,000, such as 5,000 to 13,000, or 7,000 to11,000. The polyester will typically have a hydroxy value of from 0 to200 mg KOH/g resin, such as from 30 to 70, or about 40, and an acidvalue of less than about 10, such as less than 5.

Any polyols known to be suitable for making the polyesters can be usedto form the polyester component of the present compositions. Examplesinclude but are not limited to alkylene glycols, such as ethyleneglycol, propylene glycol, diethylene glycol, dipropylene glycol,triethylene glycol, tripropylene glycol, hexylene glycol, polyethyleneglycol, polypropylene glycol and neopentyl glycol; hydrogenatedBisphenol A; cyclohexanediol; 1,3-propane diol; glycol; 1,4-butane diol;1,3-butane diol; butyl ethyl propane diol; trimethyl pentane diol;cyclohexanedimethanol; caprolactonediol, for example, the reactionproduct of epsilon-caprolactone and ethylene glycol; hydroxy-alkylatedbisphenols; polyether glycols, for example, poly(oxytetramethylene)glycol and the like. Polyols of higher functionality may also be used inlimited quantity, provided they have no adverse effects on flexibility.Examples include trimethylolpropane, trimethylolethane, pentaerythritol,tris-hydroxyethylisocyanurate and the like.

Similarly, any mono or polyacid known for use in the preparation ofpolyesters can be used to prepare the polyester polymer component of thepresent invention, and can include, for example, monomeric carboxylicacids or anhydrides having 2 to 18 carbon atoms per molecule. Examplesinclude phthalic acid, isophthalic acid, 5-tert-butyl isophthalic acid,endomethylene tetrahydrophthalic acid, tetrachlorophthalic anhydride,chlorendic acid, naphthalene dicarboxylic acid, terephthalic acid,tetrahydrophthalic acid, hexahydrophthalic acid, methylhexahydrophthalicacid, 1,3-cyclohexane dicarboxylic acid, 1,4-cyclohexane dicarboxylicacid, adipic acid, azelaic acid, sebacic acid, maleic acid, fumaricacid, itaconic acid, succinic acid, glutaric acid, decanoic diacid,dodecanoic diacid and other dicarboxylic acids of various types. Thepolyester may include minor amounts of monobasic acids such as benzoicacid, stearic acid, acetic acid and oleic acid. Also, there may beemployed higher carboxylic acids, such as trimellitic acid andtricarballylic acid. Where acids are referred to above, it is understoodthat anhydrides thereof that exist may be used in place of the acid.Also, lower alkyl esters of diacids such as dimethyl glutarate anddimethyl terephthalate can be used.

In one embodiment, the present polyester components are unsaturated.While any unsaturated polyester can be used according to the presentinvention, a particularly suitable polyester is formed from butanediol,ethylene glycol, cyclohexane dicarboxylic acid, isophthalic acid andmaleic anhydride. This embodiment is particularly suitable when a graftcopolymer is made between the polyester and acrylic copolymer; maleicanhydride, which is not typically incorporated into the polyesters,promotes grafting with the acrylic copolymer. Maleic acid, fumaric acidand/or itaconic acid and/or the anhydrides of these acids can also beused instead of or in addition to maleic anhydride to produce polyestersthat also have components particularly suitable for graft promotion. Incertain instances, the polyester of this embodiment is also particularlydesirable, as all of the components of the polyester are approved by theUnited States Food and Drug Administration (“FDA”) for direct foodcontact; these components are also listed on the European Inventory ofExisting Commercial Substances (“EINECS”).

In one embodiment, the polyester is made with excess polyol as comparedwith acid so as to produce a polyester that has hydroxy functionality.The polyester can also be prepared so as to either lack or have acidfunctionality.

Various acrylic monomers can be combined to prepare the acryliccopolymer used in the present invention. Examples includemethyl(meth)acrylate, ethyl(meth)acrylate, butyl(meth)acrylate,2-ethylhexyl(meth)acrylate, (meth)acrylic acid, vinyl aromatic compoundssuch as styrene and vinyl toluene, nitriles such as (meth)acrylonitrile,and vinyl esters such as vinyl acetate. Any other acrylic monomers knownto those skilled in the art could also be used. The term“(meth)acrylate” and like terms are used conventionally and herein torefer to both methacrylate and acrylate. A particularly suitable acryliccopolymer is formed with styrene, butyl acrylate, ethylhexyl acrylateand methacrylic acid, either alone or in further combination withhydroxyethyl methacrylate and methylmethacrylate. Again, in certaininstances this acrylic copolymer comprises components approved by theFDA for use with food cans, and listed on EINECS. Typically, the Mw ofthe acrylic copolymer will range from about 10,000 to 250,000, such as20,000 to 150,000, or 25,000 to 100,000.

As discussed above, the acrylic copolymer and polyester used in thepresent composition can be treated in any manner so as to render the twocompatible. By “compatible” is meant that the polyester and the acryliccopolymer may be combined together in a coating without phaseseparation, thus forming a homogeneous product. Compatibilizedcopolymers can simply be blended together. In this blended embodiment,the acrylate copolymer used according to the present invention does nothave pendant glycidyl groups when the polyester is acid terminated, andthe acrylate copolymer does not have pendant hydroxy groups when thepolyester is hydroxy terminated. Compatibilization can be achieved, forexample, by using an acrylic copolymer having an Mw similar to the Mw ofthe polyester (i.e. within about 1,000). Various functional groups canalso be added to the acrylic and/or polyester to compatibilize the two.For example, the acrylic copolymer can have N-(N-butoxymethyl)acrylamide(“NBMA”) functionality. When the acrylic has been functionalized withNBMA, it preferably has an Mw of about 20,000 or less. Othercompatibilizing functional groups include acid functional groups,hydroxy groups, amide groups and the like. Appropriate solvents referredto in the art as “coupling solvents” can also aid in compatibilization.An example is ethylene glycol monobutyl ether, commercially available asButyl Cellosolve from Dow Chemical.

The acrylate copolymer and polyester can also be compatibilized, forexample, by forming interpenetrating polymer networks. The preparationof such networks is described, for example, in U.S. Pat. No. 6,228,919,incorporated by reference herein.

Another method by which the polyester and acrylate copolymer can becompatibilized is through the formation of a graft copolymer. A graftcopolymer can be formed using techniques standard in the art. In onemethod, the polyester is prepared according to conventional methodsusing the materials described above. The acrylic monomers are then addedto the polyester. The acrylic can then be polymerized using a standardfree radical initiator. In this manner, the acrylate copolymer isgrafted to the already-made polyester.

Alternatively, the polyester can be grafted to an already-made acryliccopolymer. In this embodiment, a maleic anhydride group can bepolymerized in the acrylic copolymer and, subsequently, hydroxyl groupsfrom the polyester can be allowed to react with the acrylic to create agraft copolymer; the result will be an acrylic copolymer havingpolyester moieties grafted thereto.

In the methods for grafting according to the present invention, oneselects a moiety to be incorporated into the polyester and a monomer tobe included with the acrylate monomers that will react with each other.A particularly suitable example uses maleic anhydride in the formationof a polyester and styrene as one of the acrylic monomers. In thisembodiment, the styrene will react with the maleic anhydride; theacrylic copolymer will grow off of the styrene through the formation offree radicals. The result will be a polyester having acrylic copolymersgrafted thereto. It will be appreciated that not all of the acrylic andpolyester will graft; thus, there will be some “neat” polyester and some“neat” acrylate copolymer in the solution. Enough of the acrylatecopolymer and polyester will graft, however, to compatibilize the twonormally incompatible polymers.

It will be appreciated that maleic anhydride and styrene are offered asexamples of two components that will promote grafting between thenormally incompatible polymers, but that the invention is not solimited. Other compounds such as fumaric acid/anhydride or itaconicacid/anhydride may be incorporated into a polyester for grafting with astyrene containing acrylic. Other moieties that will promote graftingbetween the polyester and acrylic can also be used. Any group ofcompounds can be used for this purpose. All of these compounds arereferred to herein as “graft promoting components”. The amount of graftpromoting component used in each of the polyester and/or acrylateportions can affect the final product. If too much of these componentsare used, the product can gel or be otherwise unusable. Thegraft-promoting components should therefore be used in an amounteffective to promote grafting but not to cause gelling. Enough graftingshould be effected to allow the polyester and acrylate polymers to becompatible. In the maleic anhydride/styrene example, usually 2 to 6weight percent maleic with 8 to 30 weight percent styrene can be used,with weight percent being based on the weight of the polyester and theweight of the acrylic, respectively.

The Mw of the graft copolymer will typically be from about 3000 to250,000, such as from about 5000 to 125,000, or from about 30,000 to50,000.

The weight ratio of polyester to acrylic in the present compositions canvary widely. For example, the polyester to acrylic ratio can range from95:5 to 20:80. It has been determined that varying the amount ofpolyester in the composition will affect the amount of flexibility. Aparticularly suitable ratio of polyester to acrylic for use in coatingfood cans is 70:30, which gives a relatively flexible product that stillhas suitable acid resistance.

The acrylate copolymer and polyester in either the blended or graftedforms described above are further used in conjunction with acrosslinker. A suitable crosslinker can be determined based upon theneeds and desires of the user, and can include, for example, melaminecrosslinkers, and phenolic crosslinkers. Melamine crosslinkers arewidely commercially available, such as from Cytec Industries, Inc. asCYMEL 303,1130, 325, 327 and 370. Phenolic crosslinkers include, forexample, novolacs, resoles, and bisphenol A. Preferred for use on foodcans are phenolic resoles that are not derived from bisphenol A.

The compositions of the present invention also comprise a solvent.Suitable solvents include esters, glycol ethers, glycols, ketones,aromatic and aliphatic hydrocarbons, alcohols and the like. Particularlysuitable are zylenes, propyleneglycol monomethyl acetates, and dibasicesters such as dimethyl esters of adipic, glutaric and succinic acids.Typically, the compositions are prepared so as to be between about 30and 50 weight percent solids.

The compositions of the present invention can also contain any otherconventional additives such as pigments, colorants, waxes, lubricants,defoamers, wetting agents, plasticizers, fortifiers and catalysts. Anymineral or sulfonic acid catalyst can be used. Particularly preferredfor food can applications are phosphoric acid and dodecyl benzenesulfonic acid.

The present invention is further directed to a method for coating foodcans comprising applying any of the compositions described above to thefood can. More specifically, these compositions comprise a polymer, anacrylic copolymer, a crosslinker, one or more solvents and optionallyone or more conventional additives. The polyester and acrylic copolymercan be made compatible by any means described above such as usingblending techniques known in the art, interpenetrating networks, or thenovel graft copolymerizations described herein. The coating compositioncan be applied to the food can by any means known in the art such asroll coating, spraying, and electrocoating. It will be appreciated thatfor two-piece food cans, the coating will typically be sprayed after thecan is made. For three-piece food cans, on the other hand, a coil orsheet will typically be roll coated with one or more of the presentcompositions first and then the can will be formed.

After application, the coating is then cured. Cure is effected bymethods standard in the art. For coil coating, this is typically a shortdwell time (i.e. 9 seconds to 2 minutes) at high heat (i.e. 485° F. peakmetal temperature); for coated metal sheets cure is typically longer(i.e. 10 minutes) but at lower temperatures (i.e. 400° F. peak metaltemperature).

Any material used for the formation of food cans can be treatedaccording to the present methods. Particularly suitable substratesinclude tin-plated steel, tin-free steel, and black-plated steel.

The coatings of the present invention can be applied directly to thesteel, without any pretreatment or adhesive aid being added to the metalfirst. In addition, no coatings need to be applied over top of thecoatings used in the present methods.

The compositions of the present invention perform as desired both in theareas of flexibility and acid resistance. Significantly, these resultscan be achieved with an epoxy-free composition. Thus, the presentinvention provides particularly desirable compositions and methods forcoating food cans, which avoid performance and health issues raised byother coatings and methods reported in the art.

In addition, the present invention provides methods for compatibilizinga polyester and an acrylic. These methods are discussed above andinclude, for example, the use of an acrylamide in the formation of theacrylic copolymer, and the graft copolymerization of an acrylic onto apolyester or a polyester onto an acrylic.

As used herein, unless otherwise expressly specified, all numbers suchas those expressing values, ranges, amounts or percentages may be readas if prefaced by the word “about”, even if the term does not expresslyappear. Also, any numerical range recited herein is intended to includeall sub-ranges subsumed therein. As used herein, the term “polymer”refers to oligomers and both homopolymers and copolymers, and the prefix“poly” refers to two or more.

EXAMPLES

The following examples are intended to illustrate the invention, andshould not be construed as limiting the invention in any way.

Example 1

Polyester Polymer “A” was made as follows: TABLE 1 Ingredients Parts byWeight Charge #1 2-Methyl-1,3-Propanediol 2.4 Ethylene Glycol 1.01,6-Hexane Diol 3.6 Terephthalic Acid 7.1 Dibutyltin Oxide 0.035 Charge#2 Isophthalic Acid 3.0 Maleic Anhydride 0.54 Ionol 0.018 Charge #3Xylene 0.81 Charge #4 Xylene 5.8

Charge #1 was added to a 5-liter, 4 necked flask equipped with a motordriven stainless steel stir blade, a packed column connected to awater-cooled condenser and a heating mantle with a thermometer connectedthrough a temperature feedback control device. The reaction mixture washeated to 195° C. for six hours during which time 1.3 parts waterdistilled off. The mixture was cooled briefly to 180° C., Charge #2 wasadded and the mixture again heated at 195° C. for four hours. After thishold, the reaction was cooled. Charge #3 was added, the packed columnreplaced with a Dean-Stark, and the mixture heated to reflux (190° C.).Heating continued for seven hours during which additional waterazeotroped off. When the Acid Value of the solution was less than 1.5,the mixture was cooled to 150° C. and the resin thinned with Charge #4.

Example 2

Polyester Polymer “B” was made as follows: TABLE 2 Ingredients Parts byWeight Charge #1 1,3-Butylene Glycol 10.0 Ethylene Glycol 1.9 Charge #21,4-Cyclohexanedicarboxylic 14.5 Acid Isophthalic Acid 6.0 MaleicAnhydride 1.0 Dibutyltin Oxide 0.067 Methyl Hydroquinone 0.0029 Charge#3 Xylene 1.5 Charge #4 Xylene 10.8

Charge #1 was added to a 5 liter, 4 necked flask equipped with a motordriven stainless steel stir blade, a packed column connected to awater-cooled condenser and a heating mantle with a thermometer connectedthrough a temperature feedback control device. The reaction mixture washeated to 125° C. Charge #2 was added to the mixture and then heated to155° C. Distillation of water began and continued for 3.5 hours. Thetemperature was increased to 175° C. for 90 minutes and then to 195° C.for four hours. The reaction temperature was increased to 200° C. for3.5 hours where the distillation of water began to significantly slow.The reaction mixture was cooled to 180° C., the packed column replacedwith a Dean-Stark and a nitrogen sparge was started. Charge #3 was addedand the reaction was heated to 195° C. for seven hours at which time theacid value was less than 2.0. The resin was cooled to 80° C. and thenthinned with Charge #4.

Example 3

Acrylic Polyester Copolymer “A” was made as follows: TABLE 3 IngredientsParts by Weight Charge #1 Toluene 12.9 SOLVESSO 150¹ 11.0 Charge #2Xylene 6.0 VAZO 67² 2.0 Charge #3 Butyl Acrylate 12.0 2-HydroxyethylMethacrylate 11.2 Methacrylic Acid 1.0 Styrene 6.0 2-Ethylhexyl Acrylate4.0 Methyl Methacrylate 5.8 Polyester A from Example 1 135.3 Charge #4VAZO 67 0.1 Xylene 0.4 Charge #5 SOLVESSO 150 17.9¹Aromatic hydrocarbon mixture that boils at 150° C. used as a solvent,from Exxon Chemical America.²Azobis 2,2′-(2-methylbutyronitrile), from E. I. duPont de Nemours &Co., Inc.

Charge #1 was added to a 3 liter, 4 necked flask equipped with a motordriven stainless steel stir blade, water-cooled condenser and a heatingmantle with a thermometer connected through a temperature feedbackcontrol device. The contents of the flask were heated to reflux (128°C.). Addition of Charge #2 (over 190 minutes) began followed by theaddition of Charge #3 (over 180 minutes) five minutes later. During thefeeds, the reflux temperature gradually rose to 138° C. After theadditions were complete, the reaction was held at 138° C. for one hour.Charge #4 was added over 10 minutes and the mixture was held at 138° C.for an additional hour. The resin was thinned with Charge #5.

Example 4

Acrylic Polyester Copolymer “B” was made as follows: TABLE 4 IngredientsParts by Weight Charge #1 SOLVESSO 150 8.0 Charge #2 SOLVESSO 150 6.3Di-t-Butylperoxide 1.0 Charge #3 Butyl Acrylate 12.0 Methacrylic Acid1.0 Styrene 2.0 2-Ethylhexyl Acrylate 5.0 Polyester B 67.3 (46.8 solid)Charge #4 SOLVESSO 150 0.45 Di-t-Butylperoxide 0.026 Charge #5 SOLVESSO150 0.45 Di-t-Butylperoxide 0.026 Charge #6 SOLVESSO 150 0.45Di-t-Butylperoxide 0.026 Charge #7 SOLVESSO 150 0.45 Di-t-Butylperoxide0.026 Charge #8 Xylene 8.7

Charge #1 was added to a 2 liter, 4 necked flask equipped with a motordriven stainless steel stir blade, water-cooled condenser and a heatingmantle with a thermometer connected through a temperature feedbackcontrol device. The contents of the flask were heated to reflux (150°C.). Addition of Charges #2 and #3 were started simultaneously andcontinued over three hours. After the additions were complete, thereaction was held at 150° C. for 30 minutes. Charges #4, 5, 6 and 7 werethen added to the mixture in 30-minute increments. After Charge #7 wasadded, the mixture was held for 30 additional minutes, was cooled to130° C. and Charge #8 was added.

Example 5

Acrylic Polyester Copolymer “C” was made as follows: TABLE 5 IngredientsParts by Weight Charge #1 SOLVESSO 150 10.1 Toluene 10.1 Charge #2Xylene 3.1 VAZO 67 2.0 Charge #3 Butyl Acrylate 12.0 Methacrylic Acid1.0 Styrene 6.0 2-Ethylhexyl Acrylate 4.0 2-Hydroxyethyl Acrylate 11.2Methyl Methacrylate 5.8 Polyester B 14.4 (10.0 solid) Charge #4 Xylene0.31 VAZO 67 0.10 Charge #5 Xylene 6.7

Charge #1 was added to a 2 liter, 4 necked flask equipped with motordriven stainless steel stir blade, water cooled condenser and a heatingmantle with a thermometer connected through a temperature feedbackcontrol device. The contents of the flask were heated to 128° C.Addition of Charge #2 (over 190 minutes) followed by Charge #3 (over 180minutes) five minutes later. After the additions were complete, thereaction was held at 150° C. for 30 minutes. During the additions, thetemperature was gradually increased reflux at 138° C. After theadditions were complete, the reaction was held at 138° C. for 90minutes. Charge #4 was then added over 10 minutes followed by a one hourhold at 138° C. The resin was then thinned with Charge #5 and thencooled.

Example 6

Three different samples were prepared by charging copolymers A, B, andC, prepared as described in Examples 3, 4 and 5 respectively, intoindividual containers and mixing in the following ingredients in theorder shown under ambient conditions until homogeneous. TABLE 6Ingredient Sample 1 Sample 2 Sample 3 Copolymer A 65.9 grams 0 0Copolymer B 0 65.9 grams 0 Copolymer C 0 0 65.9 grams Phenoliccrosslinker³ 2.8 2.8 2.8 Phenolic crosslinker⁴ 8.3 8.3 8.3 Catalyst⁵ 1.11.1 1.1 Wax dispersion⁶ 3.3 3.3 3.3 Solvent⁷ 9.3 9.3 9.3 Solvent⁸ 9.39.3 9.3 Total 100 100 100³GPRI 7590 modified phenol-cresol-formaldehyde resin, from GeorgiaPacific.⁴HARZ 6572 LB para-t-butyl phenol-formaldehyde resin, from Bakelite.⁵ADDITOL XK-406 solution of a cresol-formaldehyde resin and phosphoricacid, from Solutia.⁶Luba-Print P1 solution of lanolin wax, from L. P. Bader & Co. GmbH.⁷DOWANOL PM Acetate, propylene acetate glycol monomethylether, from DowChemical.⁸SOLVESSO 150.

Coatings were prepared by drawing Samples 1-3 and a commerciallyavailable epoxy liner for food cans (Eurogold XF 12040, from PPGIndustries, Inc.) over tin plated steel (E.T.P.) sheets with a #12wire-wound rod. The coatings were baked for 10.5 minutes at 400° F. Thedrying coating weights were 4.0 mgs/sq.in.

The coated sheets were evaluated for flexibility by bending and stampingwedges (2.0 inch by 4.5 inches), stamping 300 food can ends, and bydrawing cups to 18 mm and 26 mm depths with one and two stages ofdrawing, respectively. For wedge bends and drawn cups, the percent ofcoating that remained crack-free along the bend radius (for wedge bends)and along the drawn lengths (for cups) was determined. For the stamped300 ends, the measured current (in mA) was determined using a WACOenamel rater (obtained from Wilkens-Anderson Company) in 4 sec modeusing an electrolyte solution of 7.0 grams of potassium ferrocyanurate,5.4 grams of sodium chloride, 0.5 grams of sodium sulfosuccinate, and1000 grams of water. The resistance properties of the coated stampedends and drawn cups were evaluated by processing (retorting) them inthree food simulants and measuring their ability to resist current(stamped ends) and cracking (drawn cups) after one hour in a sterilizerunder 266° F./30 psi conditions. The three simulants were tap water, a1% by weight solution of sodium chloride in tap water, and a 1% byweight solution of lactic acid in tap water. All of the results arepresented in Table 7. TABLE 7 Commercial Epoxy Sample 1 Sample 2 Sample3 Flexibility Tests. 1. Wedge Bend (% crack-free)  86%  93%  92%  73% 2.Enamel Rater of 300 ends (mA) 2 mA 2 mA 7 mA  20 mA 3. 18 mm Drawn Cup(% crack-free) 100% 100% 100% 100% 4. 26 mm Drawn Cup (% crack-free)100% 100% 100% 100% Resistance Tests. (60 mins @ 130° C.) 1. Change inEnamel Rater of 300 ends tested in: a. water 1 mA 1 mA 6 mA >200 mA b.1% salt (aq.) 2 mA 2 mA 7 mA >200 mA c. 1% lactic acid (aq.) 2 mA 2 mA20 mA  >200 mA 2. 18 mm Drawn Cup (% crack-free) tested in: a. water100% 100% 100% 100% b. 1% salt (aq.) 100% 100% 100% 100% c. 1% lacticacid (aq.) 100% 100% 100% 100% 3. 26 mm Drawn Cup (% crack-free) testedin: a. water  31% 100% 100%  19% b. 1% salt (aq.)  38%  58% 100%  23% c.1% lactic acid (aq.)  46%  38% 100%  19%

As can be seen from Table 7, Sample 1 had better results than did acurrent, epoxy-containing food can liner. Sample 2 also had very goodresults, especially acid resistance. Both Samples 1 and 2 had polyesterto acrylic ratios of about 70:30. Sample 3, which had a polyester toacrylic ratio of 20:80 demonstrates that some flexibility can be lostwith lower levels of polyester.

Whereas particular embodiments of this invention have been describedabove for purposes of illustration, it will be evident to those skilledin the art that numerous variations of the details of the presentinvention may be made without departing from the invention as defined inthe appended claims.

1. A method for coating the inside of a food can comprising applying tothe can a composition comprising: (a) a polyester; (b) an acryliccopolymer; (c) a crosslinker; and (d) a solvent, wherein the polyesterand acrylic copolymer have been blended together, having been graftedtogether, or have formed interpenetrating networks, but when thepolyester and acrylic copolymer have been blended, the acrylic copolymerdoes not have pendant glycidyl groups when the polyester is acidterminated and the acrylic copolymer does not have pendant hydroxygroups when the polyester is hydroxy terminated.
 2. The method of claim1, wherein the polyester and acrylic copolymer are grafted together. 3.The method of claim 2, wherein the acrylic copolymer is grafted to thepolyester.
 4. The method of claim 2, wherein the polyester is grafted tothe acrylic copolymer.
 5. The method of claim 1, wherein the polyesteris unsaturated.
 6. The method of claim 1, wherein the polyestercomprises maleic acid or anhydride and the acrylic copolymer comprisesstyrene.
 7. The method of claim 1, wherein the polyester has a hydroxyvalue of 0 to
 200. 8. The method of claim 1, wherein the polyester has ahydroxy value of 30 to
 70. 9. The method of claim 1, wherein thepolyester has an acid value of less than
 5. 10. The method of claim 2,wherein the graft copolymer has a weight average molecular weight of3000 to 250,000.
 11. The method of claim 2, wherein the graft copolymerhas a weight average molecular weight of 30,000 to 50,000.
 12. Themethod of claim 2, wherein the polyester comprises the reaction productof butanediol, ethylene glycol, cyclohexane dicarboxylic acid,isophthalic acid and maleic acid and/or anhydride.
 13. The method ofclaim 2, wherein the acrylic copolymer comprises styrene, butylacrylate, ethylhexylacrylate and methacrylic acid.
 14. The method ofclaim 2, wherein the acrylic copolymer comprises maleic acid and/oranhydride.
 15. The method of claim 1, wherein the crosslinker is or isderived from melamine.
 16. The method of claim 1, wherein thecrosslinker is or is derived from a resole or novalac that does notcontain bisphenol A.